1. Field of the Invention
The present invention relates to a capacitor of semiconductor integrated circuit and method for fabricating the same, and more particularly to a capacity of semiconductor integrated circuit having a structure of a metal insulator metal (MIM) type which is applied to a logic circuit or an analogue circuit and a method for fabricating the same.
2. Description of Related Art
A conventional semiconductor integrated circuit is classified in response to a signal process mode as a digital type of integrated circuit (what is called a logic circuit) in which an output signal is changed to an on/off type by a variation of input signal and an analog type of integrated circuit (what is called an analog circuit) in which an output signal linearly varies with a variation of input signal.
Since the above-mentioned integrated circuits serve to memorize information in response to whether or not charge in capacitor is present without distinction between a digital type and an analog type, in order to maintain normal operation characteristic of the circuits, a capacitor must be fabricated lest its capacitance vary with the variation of temperature or voltage while its device is manufactured.
FIG. 1 shows a cross sectional view for illustrating a capacitor structure of a conventional logic circuit or analog circuit having a gate linear width of 0.5 .mu.m which has been commonly applied when the integrated circuit is manufactured.
Referring to FIG. 1, in the conventional PIP-type capacitor of logic or analog circuit, field oxide layer (not shown) formed on the semiconductor substrate 10 is formed thereon with a lower electrode 12 made of polysillicon, on which dielectric layer 14 having an ON structure (for example, buffer oxide layer 14a/nitride layer 14b) is formed, and the dielectric layer 14 is formed thereon with an upper electrode 18 made of polycide and having a line width narrower than that of the lower electrode 12.
However, in case the capacitor of a logic or analog circuit is formed in the PIP type structure mentioned in the above, the following problem is occured.
Since the PIP type capacitor shown in FIG. 1 has the voltage coefficient of capacitance (VCC) of about 220 part per million/V (ppm) and temperature coefficient of capacitance (TCC) of about 120 ppm/C, there are problems in that a variation of the capacitance caused by a variation of voltage or temperature is increased, thereby a distribution variation of capacitance is increased as well as bad array matching characteristics appears.
Furthermore, in case the capacitor having capacitance characteristics mentioned in the above is used in a high frequency band, semiconductor integrated circuit cannot be normally operated in a stable state because resistance of polysilicon forming electrodes of capacitor is high.
To solve the problems, recently, there is a tendency to adapt the MIM structure instead of PIP structure to a capacitor when logic or analog circuit is designed. For example, as shown in FIG. 2, U.S. Pat. No. 5,406,447 discloses the MIM-type capacitor of the conventional logic or analog circuit.
Referring to FIG. 2, in the conventional MIM-type capacitor, a semiconductor substrate 20 is formed thereon with an isolation oxide film 22, the isolation oxide film 22 is formed on its predetermined portion with a lower electrode 24 made of conductive material, the lower electrode 24 is formed on its predetermined portion with a dielectric film 28 made of oxide, where a first barrier metal film 26 is formed therebetween, an intermediate film 30 is formed on the respective films, the intermediate isolation film 30 is formed therein with via holes so that the surface of the dielectric film 28 is exposed in its predetermined portion, and the intermediate film 30 is formed thereon with a second barrier metal film 32 which is formed thereon with an upper electrode 34 made of conductive material.
Such capacitor having a MIM-type structure can be more stably operated in a high frequency band than a PIP-type capacitor. In this case, however, the following problem is occured because it is difficult to monitor when etch is completed during the formation of via holes.
Since the intermediate isolation film 30 is commonly formed with about 10,000 .ANG. in thickness, 30 to 40% of the thickness in the lower film is over-etched during the formation of the via holes. Accordingly, in case the MIM-type capacitor is manufactured so as to have the structure mentioned in the above, the dielectric film 28 is also partly etched when the intermediate isolation film 30 is etched. At this time, since it is difficult to detect how much the dielectric film 28 is over-etched and accordingly thickness of the dielectric film 28 cannot be revived in the same manner, there is a problem in that the VCC value and TCC value become increased due to the variation of capacitance.
In order to solve the problem, the capacitor must be manufactured so that the dielectric film is thicker than that of the conventional dielectric film, or a separate film which can be used as a dielectric film as well as etch-stopper is further formed on the dielectric film 28, thereby the over-etch of the dielectric film 30 may be prevented during the etch of the intermediate isolation film 30. However, in case the dielectric film becomes thicker, since the capacitance becomes decreased, there is a problem in that the chip size must be increased. In case the additional film is formed, there is a problem in that material which can be used as a dielectric film and etch-stopper has not yet been developed. Therefore, the two methods cannot be applied at present time.
In case VCC and TCC values become increased, bad characteristics of capacitor is caused thereby and bad operation of analog circuits is accordingly caused. In some cases, lowered bit resolution prevents high performance of analog circuits from being realized.